This invention relates generally to pneumatic tires for passenger cars and more particularly to tires for use on high performance vehicles.
A modern trend is for the tread pattern, formed by grooves and lands in the ground contacting tread portion of a tire to be directional. A directional tire is a tire having a tread pattern such that when the tire is rotated in one direction it has different tractional properties with the ground than when it is rotated in the other direction. A typical directional tread pattern has lateral grooves that are arranged to form a series of "V" shaped grooves all pointed in the same direction around the tire tread. Usually for maximum traction grip during acceleration of high performance cars the "V" shaped grooves are pointed in the direction of travel, so that the mid portion of each "V" shaped groove will enter the footprint of the tire first.
Typical examples of this type of tire are illustrated in European Patent Application No. 0 064 934 A, British Patent Application No. GB 2 046 188 A, and U.S. Pat. No. 4,057,089.
The differences in the tractional properties between the two directions of rotation can be varied by a number of different design parameters, for example the angle of the "V" shaped grooves make relative to the mid-circumferential plane of the tire, the circumferential spacing between the "V" shaped grooves, and the land-to-sea ratio of the tread.
The present invention provides a directional tire in which the tractional properties between the two directions of rotation can be varied by an alternative parameter.